Exciter circuits are used on jet aircraft and in other applications to supply high voltage spark energy to an igniter which creates a spark in the jet engine's combustion chamber to initiate and/or maintain combustion within the engine. Traditional jet aircraft exciter circuits are well known in the art and are typically designed to utilize a low voltage supply to generate the high voltage output needed to create the spark. Numerous direct flyback, capacitive discharge, and hybrid ignition circuits have been proposed over the years. These systems typically include an exciter circuit that is connected to the igniter via a high-energy cable or ignition wire capable of carrying the high voltage and high currents necessary to produce the spark. The exciter circuit is often located close to the igniter so as to avoid the need for long runs of these high-energy cables.
The exciter circuits themselves can be implemented using various circuit designs, as noted above. For example, the exciter may include a charging circuit together with an output discharge circuit that stores energy from the charging circuit for use in creating the spark. The charging circuit commonly includes an inductive device, such as a fly-back transformer, for providing a high voltage pulse to an energy storage device, such as a capacitor, located in the discharge circuit. The discharge circuit can further include a switching device, such as a spark gap or SCR, located in series between the energy storage device and an igniter plug such that they are isolated from each other by the switching device. When the switching device is closed, it acts as a short and the stored energy is discharged across the igniter plug, thereby creating the spark.
When used in aircraft applications, the exciter circuits must meet certain performance requirements regarding electromagnetic interference (EMI) and lightning protection. In order to meet these requirements, the exciter circuit is typically housed within a protective enclosure that provides lighting protection and EMI isolation. Since the exciter circuits are normally located at the aircraft engine, such as out on the aircraft wing, these protective devices or features are separate and independent of similar devices already being used to shield and protect other electrical circuitry located at other places within the aircraft. Also, because the high-energy cables involved may carry anywhere from 600–2000 amps of electrical current, the shielding requirements addressing EMI radiation from the cables may be quite extensive, thereby increasing the cost of the system.